A diaphragm valve including a body provided with a fluid passage, a seat formed on the body and arranged at a peripheral edge of the fluid passage formed in the body so as to be demountably mountable, a disc-shaped diaphragm configured to open and close the fluid passage by being pressed against and moved away from the seat, and an upward and downward moving means configured to move a diaphragm holder configured to press a center portion of the diaphragm is known (Patent Literature 1 and the like).
Such a diaphragm is configured to seal an opening of an upward-facing depressed portion provided in the body by being fixed to the body at an outer peripheral portion thereof is resiliently deformable (vertically movable) with respect to the outer peripheral portion at a center portion thereof, and contributes to opening and closing of the fluid passage by being resiliently deformed in association with the vertical movement of a valve rod.
The diaphragm is formed, for example, of a nickel alloy thin plate, and is formed into an inverted dish shape by cutting out into a circular shape and causing a center portion thereof to protrude upward. The diaphragm may formed of a stainless steel thin plate, or of a laminated member composed of the stainless steel thin plate and a nickel-cobalt alloy thin plate. A diaphragm formed of PTFE is also known.